The present invention relates to apparatus and methods for connecting inner crossovers together on a rotor coil and, more particularly, to a support clip for supporting a crossover connecting adjacent coils of a rotor.
A generator typically includes a shaft and rotor body supported by the shaft. The rotor body defines a number of poles, which vary in number depending on the design of the generator. For example, the speed at which the shaft rotates and frequency of electric current to be produced impact the number of poles used in the generator. In a generator, copper wire is wound along the poles on the rotor body and are referred to as the winding. In most large generators, for example, such as those used in power generation plants and other similar generator applications, the cooper wire can be formed as flat, stiff, coiled copper bars. In some cases, the copper winding is about 1 by 0.25 inches in cross-section, as one non-limiting example. These coils forming the winding are often referred to as the conductors.
The winding is designed to form a complete circuit from a first pole to the last pole. Because the winding is formed from a stiff material in these large generators, the winding ends are connected between adjacent poles with conductive jumpers known as rotor pole crossovers.
Rotor pole crossovers are designed in many shapes and sizes and change in design as the generator design requirements dictate. For example, some rotor pole crossovers have been designed as rings that encircle the shaft. Other rotor pole crossovers are designed as short crossovers in the form of flat plates or reverse S-shapes, which are oriented to lie axially relative to the rotor shaft. During generator operation, large centrifugal forces are exerted on the winding and rotor pole crossover, for example, by daily starts and stops to accommodate peak on and off electrical generation demands. As a result, the rotor pole crossovers undergo stressful duty cycles. If rotor pole crossovers lack flexibility, they crack and cause a loss in the generator electrical field.
Currently, many electrical power generators use a common method for connecting the inner crossovers together on the main rotor coils. This conventional method involves bending a flat magnet wire end of one coil 90 degrees to mate with the flat magnet wire end of the neighboring coil. The two coil ends are then resistance brazed to one another. Since the 90 degree bend is unsupported, expansion and contraction of the solid bend, caused by the variable speed of the spinning rotor's centrifugal forces, result in fatigue failure of the solid wire or the brazed joint.
A flexible crossover, as disclosed, for example, in U.S. Pat. Nos. 7,247,966 and 6,930,434, may be used to reduce the failure due to thermal cycling. The flexible crossover, however, will still be affected by centrifugal forces and, thus, may still fail to provide adequate electrical connection between coils.
As can be seen, there is a need for a rotor crossover and methods that may prevent failure of the crossover due to centrifugal forces.